1. Field of the Invention
The present invention relates to injection molding machines and, more particularly, to a mechanism which is adapted for the program-controlled exchange of one injection molding die for another in the die closing unit of a plastics injection molding machine.
2. Description of the Prior Art
The changeover of an injection molding machine from the production of a given part to the production of another part requires an exchange of injection molding dies in the die closing unit and, in some cases, also an exchange of injection units.
The exchange of injection molding dies tends to necessitate a considerable amount of time machine downtime, not only for the removal of the previously used die assembly and the insertion and attachment of the new die assembly, but also for the transfer from the former to the latter of the various fluid lines and/or air hoses, as well as any electrical and other operating connections. Finally, the newly installed injection molding die needs to be preheated to the required operating temperature, before production operations can be resumed.
As part of a mechanized die exchange procedure, it has therefore already been suggested to use hydraulically operated clamping devices in the place of the conventional threaded fasteners to clamp the two die halves to their die carrier plates. Several such clamping devices are known from the prior art. An improved attachment mechanism for interchangeable injection molding dies is disclosed in my copending U.S. patent application, Ser. No. 449,550 of Dec. 13, 1982.
In a pamphlet entitled "Battenfeld-Symposium mit Sonderschau 4.-7. Mai 1982", it is further suggested to provide a horizontal transfer device in the form of a dolly, the wheels of which are supported on the factory floor. The dolly is guided for longitudinal translational movements along the machine base, carrying on its top a horizontal roller conveyor. A die assembly resting on this roller conveyor can thus be transferred horizontally into the clamping space of the die closing unit, using a drive spindle, for example.
The two die halves of the die assembly are provided with special back plates which are larger than the die plates themselves, so as to allow for a mechanized insertion and clamping of the die assembly. In the prior art device mentioned, the back plates of the two die halves form upwardly and downwardly protruding flanges with a tapered shoulder profile. The latter is engageable by a plurality of matchingly tapered clamping plungers advancing vertically from above and below against the back plate.
In order to transfer a previously used injection molding die from the die closing unit to the transfer dolly, the clamping devices have to be released by retracting the clamping plungers; then the two die halves are latched together and the movable die carrier plate is retracted to free the centering collar of the movable die half from the movable die carrier plate. This leaves the entire die assembly supported on the stationary die carrier plate, which engages and guides the back plate of the stationary die half by means of guide faces on upper and lower guide blocks which also house the clamping plungers. In this guide configuration, the die assembly is retracted horizontally, until it comes to rest on the roller conveyor of the transfer dolly. The insertion of a new die assembly requires the same steps, in reverse order, with the exception that the clamping plungers of the stationary die carrier plate are actuated, before the movable die carrier plate is approached against the die.
Such an arrangement has several shortcomings: Among them are the fact that the movable die carrier plate needs to be moved away and that, consequently, it cannot participate in the support and guidance of the die assembly during the transfer movement. The support of the assembly is therefore one-sided. The problem-free reengagement of the movable die carrier plate over the centering collar of the movable die plate is not assured. The necessary movement clearances between the guide faces of the guide blocks and the back plate of the stationary die half make it possible for the vertically moving clamping plungers to shift the die half out of position, when they execute their clamping movement.
The absence of a positively controlled transfer drive, combined with the fact that the level of the roller conveyor is determined by the engagement between the dolly wheels and the floor, independently of the machine base, preclude a programmed, fully automated exchange of injection molding dies. Furthermore, the fact that the die assembly is guided on only one of the two die carrier plates limits the application of this device to die assemblies of moderate weight.
A die transfer table is disclosed in my German Offenlegungsschrift (Publ. Application) No. 24 21 811 and corresponding U.S. Pat. No. 3,973,888. This prior art device is designed for use with an injection molding die which has a transfer portion of the die in duplicate units, for alternating insertion into the die assembly in the clamping space of a vertically operating die closing unit. While the closed die is being injected with plastic raw material in the die closing unit, the other transfer portion of the die assembly rests on the transfer table, where it is being loaded with an insert.
This device is not suitable for use with a horizontally operating die closing unit and it can therefore not be used for the program-controlled exchange of a succession of injection molding dies of non-uniform structure, particularly dies of unequal axial depth.